Microcoil vaso-occlusive device with multi-axis secondary configuration

ABSTRACT

A vaso-occlusive device includes a microcoil formed into a minimum energy state secondary configuration comprising a plurality of curved segments, each defining a discrete axis, whereby the device, in its minimum energy state configuration, defines multiple axes. In a preferred embodiment, the secondary configuration-comprises a plurality of interconnected closed loops defining a plurality of discrete axes. In a second embodiment, the secondary configuration defines a wave-form like structure comprising an array of laterally-alternating open loops defining a plurality of separate axes. In a third embodiment, the secondary configuration forms a series of tangential closed loops, wherein the entire structure subtends a first angle of arc, and wherein each adjacent pair of loops defines a second angle of arc. In a fourth embodiment, the secondary configuration forms a logarithmic spiral. In all embodiments, the device, in its secondary configuration, has a dimension that is substantially larger than the largest dimension of the vascular site (i.e., aneurysm) in which it is to be deployed. Thus, confinement of the device within an aneurysm causes it to assume a three-dimensional configuration with a higher energy state than the minimum energy state. Because the minimum energy state configuration of the device is larger (in at least one dimension) than the aneurysm, the deployed device is constrained by its contact with the walls of the aneurysm from returning to its minimum energy state configuration. The engagement of the device with the aneurysm wall minimizes shifting or tumbling due to blood flow. Furthermore, the secondary configuration is not conducive to “coin stacking,” thereby minimizing the compaction experienced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of application Ser. No.09/671,021; filed Sep. 26, 2000 now U.S. Pat. No. 6,605,101.

FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

This invention relates generally to the field of vascular occlusiondevices and methods. More specifically, it relates to an apparatus andmethod for occluding a blood vessel by embolizing a targeted site (suchas an aneurysm) in the blood vessel.

The embolization of blood vessels is desired in a number of clinicalsituations. For example, vascular embolization has been used to controlvascular bleeding, to occlude the blood supply to tumors, and to occludevascular aneurysms, particularly intracranial aneurysms. In recentyears, vascular embolization for the treatment of aneurysms has receivedmuch attention. Several different treatment modalities have beenemployed in the prior art. U.S. Pat. No. 4,819,637—Dormandy, Jr. et al.,for example, describes a vascular embolization system that employs adetachable balloon delivered to the aneurysm site by an intravascularcatheter. The balloon is carried into the aneurysm at the tip of thecatheter, and it is inflated inside the aneurysm with a solidifyingfluid (typically a polymerizable resin or gel) to occlude the aneurysm.The balloon is then detached from the catheter by gentle traction on thecatheter. While the balloon-type embolization device can provide aneffective occlusion of many types of aneurysms, it is difficult toretrieve or move after the solidifying fluid sets, and it is difficultto visualize unless it is filled with a contrast material. Furthermore,there are risks of balloon rupture during inflation and of prematuredetachment of the balloon from the catheter.

Another approach is the direct injection of a liquid polymer embolicagent into the vascular site to be occluded. One type of liquid polymerused in the direct injection technique is a rapidly polymerizing liquid,such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, thatis delivered to the target site as a liquid, and then is polymerized insitu. Alternatively, a liquid polymer that is precipitated at the targetsite from a carrier solution has been used. An example of this type ofembolic agent is a cellulose acetate polymer mixed with bismuth trioxideand dissolved in dimethyl sulfoxide (DMSO). Another type is ethyleneglycol copolymer dissolved in DMSO. On contact with blood, the DMSOdiffuses out, and the polymer precipitates out and rapidly hardens intoan embolic mass that conforms to the shape of the aneurysm. Otherexamples of materials used in this “direct injection” method aredisclosed in the following U.S. Pat. No. 4,551,132—Pásztor et al.; U.S.Pat. No. 4,795,741—Leshchiner et al.; U.S. Pat. No. 5,525,334—Ito etal.; and U.S. Pat. No. 5,580,568—Greffet al.

The direct injection of liquid polymer embolic agents has provendifficult in practice. For example, migration of the polymeric materialfrom the aneurysm and into the adjacent blood vessel has presented aproblem. In addition, visualization of the embolization materialrequires that a contrasting agent be mixed with it, and selectingembolization materials and contrasting agents that are mutuallycompatible may result in performance compromises that are less thanoptimal. Furthermore, precise control of the deployment of the polymericembolization material is difficult, leading to the risk of improperplacement and/or premature solidification of the material. Moreover,once the embolization material is deployed and solidified, it isdifficult to move or retrieve.

Another approach that has shown promise is the use of thrombogenicmicrocoils. These microcoils may be made of a biocompatible metal alloy(typically platinum and tungsten) or a suitable polymer. If made ofmetal, the coil may be provided with Dacron fibers to increasethrombogenicity. The coil is deployed through a microcatheter to thevascular site. Examples of microcoils are disclosed in the followingU.S. Pat. No. 4,994,069—Ritchart et al.; U.S. Pat. No.5,122,136—Guglielmi et al.; U.S. Pat. No. 5,133,731—Butler et al.; U.S.Pat. No. 5,226,911—Chee et al.; U.S. Pat. No. 5,304,194—Chee et al.;U.S. Pat. No. 5,312,415—Palermo; U.S. Pat. No. 5,382,259—Phelps et al.;U.S. Pat. No. 5,382,260—Dormandy, Jr. et al.; U.S. Pat. No.5,476,472—Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074—Mirigian; U.S.Pat. No. 5,582,619—Ken; U.S. Pat. No. 5,624,461—Mariant; U.S. Pat. No.5,639,277—Mariant et al.; U.S. Pat. No. 5,658,308—Snyder; U.S. Pat. No.5,690,667—Gia; U.S. Pat. No. 5,690,671—McGurk et al.; U.S. Pat. No.5,700,258—Mirigian et al.; U.S. Pat. No. 5,718,711—Berenstein et al.;U.S. Pat. No. 5,891,058—Taki et al.; U.S. Pat. No. 6,013,084—Ken et al.;U.S. Pat. No. 6,015,424—Rosenbluth et al.; and Des. 427,680—Mariant etal.

While many prior art microcoil devices have met with some success intreating small aneurysms with relatively narrow necks, it has beenrecognized that the most commonly used microcoil vaso-occlusive devicesachieve less than satisfactory results in wide-necked aneurysms,particularly in the cerebrum. This has led to the development ofthree-dimensional microcoil devices, such as those disclosed in U.S.Pat. No. 5,645,558—Horton; U.S. Pat. No. 5,911,731—Pham et al.; and U.S.Pat. No. 5,957,948—Mariant (the latter two being in a class of devicesknown as “three-dimensional Guglielmi detachable coils”, or “3D-GDC's”).See, e.g., Tan et al., “The Feasibility of Three-Dimensional GuglielmiDetachable Coil for Embolisation of Wide Neck Cerebral Aneurysms,”Interventional Neuroradiology, Vol. 6, pp. 53–57 (June, 2000); Cloft etal., “Use of Three-Dimensional Guglielmi Detachable Coils in theTreatment of Wide-necked Cerebral Aneurysms,” American Journal ofNeuroradiology, Vol. 21, pp. 1312–1314 (August, 2000).

The typical three-dimensional microcoil is formed from a length of wirethat is formed first into a primary configuration of a helical coil, andthen into a secondary configuration that is one of a variety ofthree-dimensional shapes. The minimum energy state of this type ofmicrocoil is its three-dimensional secondary configuration. Whendeployed inside an aneurysm, these devices assume a three-dimensionalconfiguration, typically a somewhat spherical configuration, that is ator slightly greater than, the minimum energy state of the secondaryconfiguration. Because the overall dimensions of these devices in theirnon-minimum energy state configuration is approximately equal to orsmaller than the interior dimensions of the aneurysm, there is nothingto constrain the device from shifting or tumbling within the aneurysmdue to blood flow dynamics.

In some of these three-dimensional devices (e.g., U.S. Pat.5,122,136—Guglielmi et al.), the secondary configuration is itself ahelix or some similar form that defines a longitudinal axis. Deviceswith what may be termed a “longitudinal” secondary configuration form athree-dimensional non-minimum energy state configuration when deployedinside an aneurysm, but, once deployed, they have displayed a tendencyto revert to their minimum energy state configurations. This, in turn,results in compaction due to “coin stacking” (i.e., returning to thesecondary helical configuration), thereby allowing recanalization of theaneurysm.

There has thus been a long-felt, but as yet unsatisfied need for amicrocoil vaso-occlusive device that has the advantages of many of theprior art microcoil devices, but that can be used effectively to treataneurysms of many different sizes configurations, and in particularthose with large neck widths. It would be advantageous for such a deviceto be compatible for use with existing guidewire and microcathetermicrocoil delivery mechanisms, and to be capable of being manufacturedat costs comparable with those of prior art microcoil devices.

SUMMARY OF THE INVENTION

Broadly, the present invention is a filamentous vaso-occlusive devicethat has a minimum energy state secondary configuration comprising aplurality of curved segments, whereby the device, in its minimum energystate configuration, defines multiple axes and/or foci. Morespecifically, each segment defines either a plane and an axis that issubstantially perpendicular to the plane, or a path around the surfaceof a sphere, wherein the path is defined by a unique locus located atthe approximate center point of the sphere around which the path isgenerated, and by a radius extending from that locus that is equal tothe radius of that sphere.

In a particular preferred embodiment, the present invention is anelongate microcoil structure having a minimum energy state secondaryconfiguration that defines a plurality or series oftangentially-interconnected closed loops, preferably substantiallycircular or elliptical, defining a plurality of separate axes. In oneform of the preferred embodiment, the closed loops are substantiallycoplanar and define axes that are substantially parallel. That is, theplanes defined by the segments are themselves substantially coplanar. Inanother form of the preferred embodiment, each pair of adjacent loopsdefines a shallow angle, whereby their respective axes define an angleof not more than about 90°, and preferably not more than about 45°,between them. A further form of the preferred embodiment has thetangential loops arranged SO that the axis defined by each loop isorthogonal to a unique radius of a circle, the radii being separated bya fixed angle of arc. In still another form of the preferred embodiment,the loops, instead of being tangential, overlap. In any of these forms,the loops may be of substantially uniform diameter, or they may be ofdifferent diameters. For example, the first and/or last loop in theseries may be of a smaller diameter than the other loops, or the loopsmay be in a series of loops of progressively decreased diameter,optionally with an additional small-diameter loop preceding the largestdiameter loop.

In first alternative embodiment, the microcoil structure has a minimumenergy state secondary configuration that defines a wave-form likestructure comprising a longitudinal array of laterally-alternating openloops defining a plurality of separate axes. In a specific constructionof this embodiment, the wave-form like structure defines a substantiallysinusoidal waveform wherein each of the maxima and minima of thewaveform defines an arc of radius r, and wherein each arc is connectedto an adjacent arc by a straight section of length L, wherein L is lessthan about 2r. As in the preferred embodiment, the alternativeembodiment may be in a first form in which the loops are substantiallycoplanar and their respective axes are substantially parallel, or in asecond form in which each pair of adjacent loops defines a shallowangle, whereby their respective axes define an angle of not more thanabout 90°, and preferably not more than about 45°, between them.

In a second alternative embodiment, the microcoil structure, in itssecondary configuration, forms a series of tangential closed loops,preferably either substantially circular or elliptical, wherein theentire structure subtends a first angle of arc, and wherein eachadjacent pair of loops defines a second angle of arc between them.Preferably, the first angle is greater than about 30°, and the secondangle is less than about half of the first angle. It will be seen thateach loop defines an axis, with the angle formed by the axes of adjacentloops being the second angle.

In a third alternative embodiment, the secondary configuration of themicrocoil structure forms preferably at least two interconnectedequiangular or logarithmic spirals, each defining a single unique axis.As used in this specification, a logarithmic or equiangular spiral isdefined as a curve that cuts all radii vectors at a constant angle.Specifically, if the curve is a spiral, that is, a curve in which theradial vector R is a monotonic increasing function of the radial angleθ, the spiral will be an equiangular spiral if the angle α formedbetween a radial vector R and the tangent for any point P on the spiralis constant. In equiangular spirals having an angle α of greater thanabout 70°, the configuration begins to resemble that of the shell of thechambered nautilus. In the limiting case, it may be seen that a circleis an equiangular spiral in which the angle α is 90° (the radial vectorbeing a radius).

In a fourth alternative embodiment, the secondary configuration of themicrocoil structure resembles a series of interconnected complex curvedsegments, each of which is defined by a path around the surface of asphere. Each of the segments is thus defined by a unique focus locatedat the approximate center point of the sphere around which the path isgenerated, and by a radius extending from that locus that is equal tothe radius of that sphere. Each segment may be defined by radii that arecoplanar (in the case of a segment that is defined by a substantiallycircumferential path around its defining sphere), or by radii that liein different planes intersecting the sphere (where path around thedefining sphere deviates from a circumferential path). The segments thusresemble nearly, but not fully, completed circles (circumferential path)or helical loops (non-circumferential path), and they may be either ofuniform or different diameters.

In any of the embodiments, the device is preferably formed from amicrocoil structure, but it may alternately be formed of a flexible,filamentous, non-coil structure. Known non-coil structures used invaso-occlusive devices include, but are not limited to, wires, slottedwires, spiral cut wires, tubes, slotted tubes, spiral cut tubes, polymerfilaments, polymer/metal composite filaments, and micro-chains.

In any of the embodiments, the device, in its minimum energy statesecondary configuration, has a dimension that is substantially larger(preferably at least about 25% greater) than the largest dimension ofthe vascular space in which the device is to be deployed. Mostpreferably, the length of the device, in its minimum energy statesecondary configuration, should be at least about twice the maximumdiameter of the targeted aneurysm or other vascular site in which thedevice is to be installed. Also, it is advantageous to provide in thedevice at least one curved segment having a diameter, in the minimumenergy state secondary configuration, that is approximately equal to thelargest diameter of the targeted aneurysm or vascular site. Thus, whenthe device is deployed inside a vascular site such as an aneurysm, theconfinement of the device within the site causes the device to assume athree-dimensional configuration that has a higher energy state than theminimum energy state. Because the minimum energy state of the device islarger (in at least one dimension) than the space in which it isdeployed, the deployed device is constrained by its intimate contactwith the walls of the aneurysm from returning to its minimum energystate configuration. Therefore, the device still engages the surroundinganeurysm wall surface, thereby minimizing shifting or tumbling due toblood flow dynamics. Furthermore, the minimum energy state secondaryconfiguration (to which the device attempts to revert) is not one thatis conducive to “coin stacking”, thereby minimizing the degree ofcompaction that is experienced.

As will be better appreciated from the detailed description thatfollows, the present invention provides for effective embolization ofvascular structures (particularly aneurysms) having a wide variety ofshapes and sizes. It is especially advantageous for use in wide-neckedaneurysms. Furthermore, as will be described in more detail below, thepresent invention may be deployed using conventional deploymentmechanisms, such as microcatheters and guidewires.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a microcoil vaso-occlusive device inaccordance with a preferred embodiment of the present invention;

FIG. 2 is a partial view of the device of FIG. 1, taken within the areadesignated by the numeral 2 in FIG. 1;

FIGS. 3 and 4 are partial views of a microcoil vaso-occlusive device inaccordance with another form of the preferred embodiment of the presentinvention;

FIG. 5 is a plan view of a microcoil vaso-occlusive device in accordancewith a first alternative embodiment of the invention;

FIG. 6 is an elevational view of the present invention in the process ofbeing deployed through a microcatheter into a wide-necked aneurysm;

FIG. 7 is a perspective view of a heat treatment fixture used tomanufacture the preferred embodiment of the present invention;

FIG. 8 is a perspective view of a second alternative embodiment of theinvention;

FIG. 9 is an elevational view of the second alternative embodiment ofFIG. 8;

FIG. 10 is a plan view of another form of the first alternativeembodiment of the invention;

FIG. 11 is a plan view of a third alternative embodiment of theinvention;

FIGS. 12–15 are plan views of other forms of the preferred embodiment ofthe invention;

FIG. 16 is a perspective view of a fourth alternative embodiment of theinvention, showing how its is formed on a specialized heat treatmentfixture, the latter being shown in a simplified, idealized form; and

FIG. 17 is an elevational view of still another form of the preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIGS. 1–4 and 8, a microcoil vaso-occlusive device10, in accordance with a preferred embodiment of the invention is shown.The device 10 comprises a suitable length of wire formed into theprimary configuration of a helical microcoil 12 (FIG. 2). Suitablematerials for the device 10 include platinum, rhodium, palladium,rhenium, tungsten, gold, silver, tantalum, and various alloys of thesemetals. Various surgical grade stainless steels may also be used.Preferred materials include the platinum/tungsten alloy known asPlatinum 479 (92% Pt, 8% W, available from Sigmund Cohn, of MountVernon, N.Y.) and titanium/nickel alloys (such as the titanium/nickelalloy known as “nitinol”). Another material that may be advantageous isa bimetallic wire comprising a highly elastic metal with a highlyradiopaque metal. Such a bimetallic wire would also be resistant topermanent deformation. An example of such a bimetallic wire is a productcomprising a nitinol outer layer and an inner core of pure referencegrade platinum, available from Sigmund Cohn, of Mount Vernon, N.Y., andAnomet Products, of Shrewsbury, Mass. Wire diameters of about 0.0125 mmto about 0.150 mm may be used.

The microcoil 12 has a diameter that is typically in the range of about0.125 mm to about 0.625 mm, with a preferred a preferred range, for mostneurovascular applications, of about 0.25 mm to about 0.40 mm. The axiallength of the microcoil 12 may be anywhere from about 5 mm to about 1000mm, with about 20 mm to about 400 mm being typical.

The primary winding of the microcoil 12 is applied under tension. Theamount of tension, and the pitch of the primary winding, determine thestiffness of the microcoil 12. These parameters can be varied along thelength of the microcoil 12 to form a microcoil having different degreesof stiffness along its length, which may be advantageous in certainapplications.

The microcoil 12 is formed into a secondary configuration that comprisesa plurality of curved segments, each defining an axis, whereby themicrocoil 12 defines multiple axes. More specifically, each of thecurved segments defines a plane an axis that is substantiallyperpendicular to the plane. In the preferred embodiment of FIGS. 1–4,the curved segments are tangentially-interconnected closed loops 14 a,14 b that are substantially circular, and that define a plurality ofseparate axes 16. In one form of the preferred embodiment, shown in FIG.1, the loops 14 a, 14 b are substantially coplanar and define axes 16that are substantially parallel. In another form of the preferredembodiment, shown in FIGS. 3 and 4, each pair of adjacent loops 14 a, 14b defines a shallow angle, whereby their respective axes 16 define anangle (θ₁, θ₂, θ₃, and θ₄) of not more than about 90° between them, andpreferably not more than about 45°.

The preferred embodiment of the invention typically includes a pair ofend loops 14 a and at least one intermediate loop 14 b. Typically, therewill be up to four intermediate loops 14 b, depending on the vascularsite to be embolized, but there may be as many as six or more, for usein very large vascular sites. The intermediate loops are sized to have adiameter approximately equal to the maximum diameter of the targetvascular site (e.g., an aneurysm), while the end loops 14 a have aslightly smaller diameter (preferably, approximately 1.5 mm smaller),for purposes to be described below.

The primary microcoil 12 is formed into the secondary configuration byheat treatment, as is well known in the art. For example, the annealedprimary coil may be initially placed into the secondary configuration bywinding or wrapping around a suitably shaped and sized mandrel ofrefractory material, and then subjected to an annealing temperature fora specified period of time. For Platinum 479, for example, an annealingtemperature of about 500° C. to about 1000° C., preferably approximately670° C., is maintained for about 30 to 90 minutes, preferably about 60minutes, then cooled to room temperature and ultrasonically cleaned. Theresultant secondary configuration is thereby made permanent, and itbecomes the minimum energy state configuration of the microcoil 12.

FIG. 7 shows a heat treatment fixture 50 used in the manufacture of thepreferred embodiment of the invention. The fixture 50 is made of arefractory material, and it includes a base 52 having a surface on whichis provided a mandrel for the secondary winding. The mandrel comprises aplurality of winding pins 54 a, 54 b extending upwardly from the surfaceof the base 52. The exemplary fixture 50 shown in the drawing has sixpins arranged in roughly a hexagonal pattern. There are two end windingpins 54 a adjacent each other, and four intermediate winding pins 54 b.A pair of fastening pegs 56 is located near one end of the fixture, forfastening the ends of the primary coil 12.

The diameters of the end winding pins 54 a are slightly smaller than thediameters of the intermediate winding pins 54 b to achieve the sizerelationships described above. The spacings between the pins 54 a, 54 bare only slightly greater than the diameter of the primary coil 12, sothat only one wind of the primary coil can be passed around the pinswith each winding of the secondary coil. Each subsequent winding of thesecondary coil is thus stacked on top of the previous winding. Thiseliminates any straight sections in the secondary coil, which, duringdeployment, would tend to push the coil into the parent artery.

During the secondary winding process, the primary coil 12 is kept undertension. The amount of tension can be adjusted to control the degree ofspring-back of the loops 14 a, 14 b of the microcoil 12.

The secondary winding of the microcoil 12 is performed so that the loops14 a, 14 b reverse direction as the microcoil 12 is wrapped around eachsuccessive pin on the fixture. This ensures that loops will not coinstack, and that they will disperse randomly throughout the aneurysm oncedeployed. Furthermore, in the preferred embodiment, each loop is wound acomplete 360° before the next loop is wound. This ensures that each loopwill completely seat within the aneurysm before the microcoil 12reverses direction. With a complete loop intact, the loop strength ismaximized, and the loop distributes loads evenly.

FIGS. 12–15 and 17 illustrate alternative forms of the above-describedpreferred embodiment. Specifically, in FIG. 12, a microcoil 12′ has asecondary configuration that includes a plurality of connected curvedsegments, wherein the curved segments are overlapping connected closedloops 14′, that are substantially circular, with each loop 14′ defininga separate axis 16′. In FIG. 13, a microcoil 12″ has a secondaryconfiguration that includes a plurality of connected curved segments,wherein the curved segments are tangentially-interconnected,substantially elliptical loops 14″, each defining a separate axis 16″.FIGS. 14 and 15 show alternative forms that are similar to that of FIGS.1–4, except that the loops are of different diameters. Thus, in FIG. 14,a microcoil 12′″ has a secondary configuration that includes a pluralityof tangentially-interconnected, substantially circular loops 14′″ ofprogressively decreasing diameter, starting from a loop 14′″c of thelargest diameter, each of the loops defining a unique axis 16′″. Thevariant form shown in FIG. 15 is similar to that of FIG. 14, except thatthere is an additional small-diameter loop 14′″d preceding the largestdiameter loop 14′″c. A further form of the preferred embodiment,illustrated in FIG. 17, comprises a microcoil 12 ^(iv) having a minimumenergy state secondary configuration in which a plurality ofinterconnected, tangential loops 14 ^(iv) are arranged so that each loopdefines an axis 16 ^(iv) that is orthogonal to a unique radius r of acircle, the radii being separated by a fixed angle of arc θ.

FIG. 5 shows a microcoil vaso-occlusion device 20 in accordance with afirst alternative embodiment of the invention. This embodiment includesa primary microcoil 22 formed into a secondary minimum energy stateconfiguration that defines a wave-form like structure comprising alongitudinal array of laterally-alternating open loops 24 defining aplurality of separate axes 26. As in the preferred embodiment, thealternative embodiment may be in a first form in which the loops 24 aresubstantially coplanar and their respective axes 26 are substantiallyparallel, or in a second form in which each pair of adjacent loops 24defines a shallow angle, whereby their respective axes 26 define anangle of not more than about 90°, and preferably not more than about45°, between them. The materials, dimensions, and method of manufactureof this alternative embodiment are, in all material respects, similar tothose of the preferred embodiment described above.

FIG. 10 illustrates a specific construction of this embodiment, whereinthe primary microcoil structure 22′ is formed into a secondary minimumenergy state configuration having a wave-form like structure thatdefines a substantially sinusoidal waveform, defining a plurality ofseparate axes 26′. The waveform has at least one maximum 22 a and atleast one minimum 22 b, each of which defines an arc of radius r, andwherein each arc is connected to an adjacent arc by a straight sectionof length L, wherein L is less than about 2r.

The method of using the present invention is shown in FIG. 6. In use,the proximal end of the microcoil 12 (or 22) is attached to the distalend of an elongate delivery device, such as a guidewire or microcatheter(not shown). The attachment may be by any of a number of ways known inthe art, as exemplified by the following U.S. patents, the disclosuresof which are expressly incorporated herein by reference: U.S. Pat. No.5,108,407—Geremia et al.; U.S. Pat. No. 5,122,136—Guglielmi et al.; U.S.Pat. No. 5,234,437—Sepetka; U.S. Pat. No. 5,261,916—Engelson; U.S. Pat.No. 5,304,195—Twyford, Jr. et al.; U.S. Pat. No. 5,312,415—Palermo; U.S.Pat. No. 5,423,829—Pham et al.; U.S. Pat. No. 5,522,836—Palermo; U.S.Pat. No. 5,645,564—Northrup et al.; U.S. Pat. No. 5,725,546—Samson; U.S.Pat. No. 5,800,453—Gia; U.S. Pat. No. 5,814,062—Sepetka et al.; U.S.Pat. No. 5,911,737—Lee et al.; U.S. Pat. No. 5,989,242—Saadat et al.;U.S. Pat. No. 6,022,369—Jacobsen et al. U.S. Pat. No. 6,063,100—Diaz etal.; U.S. Pat. No. 6,068,644—Lulo et al.; and U.S. Pat. No.6,102,933—Lee et al.

A target vascular site is visualized, by conventional means, well-knownin the art. The target vascular site may be an aneurysm 40 branching offa parent artery 42. The aneurysm 40 has a dome 44 connected to thebranch artery by a neck 46. A catheter 30 is passed intravascularlyuntil it enters the dome 44 of the aneurysm 40 via the neck 46. Themicrocoil 12 is passed through the catheter 30 with the assistance ofthe guidewire or microcatheter until the microcoil 12 enters the dome 44of the aneurysm 40.

The undersized end loop 14 a at the distal end of the microcoil 12enters the aneurysm first. This assists in seating the first loopproperly, because the smaller size keeps the first loop inside the neck46 of the aneurysm, avoiding the parent artery 42.

The intermediate loops 14 b then enter the aneurysm. Because they aresized to fit the aneurysm, they can deploy freely and smoothly withminimal friction against the wall of the aneurysm. Because the secondaryconfiguration of the microcoil 12 is essentially coplanar, all of theintermediate loops exert a force against the walls of the aneurysm dome44, thereby improving the resistance of the microcoil 12 to shifting dueto pulsatile blood flow.

As the microcoil 12 enters the aneurysm, it attempts to assume itssecondary configuration. Because the microcoil, in its secondaryconfiguration, is larger than the aneurysm, however, it is constrainedinto a deployed configuration in which it tends to line the periphery ofthe aneurysm. In this deployed configuration, the microcoil is in anenergy state that is substantially higher than its minimum energy state.Thus, when the device is deployed inside a vascular site such as ananeurysm, the confinement of the device within the site causes thedevice to assume a three-dimensional configuration that has a higherenergy state than the minimum energy state. Because the minimum energystate of the device is larger (in at least one dimension) than the spacein which it is deployed, the deployed device is constrained by itsintimate contact with the walls of the aneurysm from returning to itsminimum energy state configuration. Therefore, the device still engagesthe surrounding aneurysm wall surface, thereby minimizing shifting ortumbling due to blood flow dynamics. Furthermore, the minimum energystate secondary configuration (to which the device attempts to revert)is not one that is conducive to “coin stacking”, thereby minimizing thedegree of compaction that is experienced.

The undersized end loop 14 a at the proximal end of the microcoil 12enters the aneurysm last. After the microcoil is fully deployed, it iscontrollably detached from the delivery device by any suitable meanswell-known in the art, thereby allowing the delivery device to bewithdrawn, leaving the microcoil in place to embolize the aneurysm.After detachment, the proximal end loop 14 a curls into the neck 46 ofthe aneurysm 40, avoiding the parent artery 42.

The microcoil is designed with a maximum loops diameter that isdimensioned to line the periphery of the aneurysm upon deployment, asmentioned above. For larger aneurysms, it is advantageous to fill in asubstantial portion of the interior volume of the aneurysm by deployingone or more additional microcoils, of progressively smaller maximum loopdiameter.

FIGS. 8 and 9 illustrate a vaso-occlusion device in accordance with asecond alternative embodiment of the invention. This embodiment includesa primary microcoil 60 formed into a secondary minimum energy stateconfiguration that forms a series of tangential closed loops 62(preferably substantially circular or elliptical), wherein the entirestructure subtends a first angle of arc θ₁, and wherein each adjacentpair of circles or ellipses defines a second angle of arc θ₂ betweenthem. Preferably, the first angle θ₁ is greater than about 30°, and thesecond angle θ₂ is less than about half of the first angle θ₁. Althoughnot illustrated in the drawings, it will be appreciated that each loop62 defines an axis, whereby the angle formed between the axes ofadjacent loops 62 is equal to θ₂.

FIG. 11 illustrates a vaso-occlusive device in accordance with a thirdalternative embodiment of the invention. In this embodiment, a microcoil70 has a secondary configuration that forms at least a pair of connectedequiangular or logarithmic spirals 72, each of the spirals defining anaxis 73 that is orthogonal to the plane defined by the spiral. For thepurpose of this specification, an equiangular or logarithmic spiral isdefined as a curve that cuts all radii vectors at a constant angle,where a radial vector R is defined as a line drawn from any point P onthe spiral to the center of the spiral. Specifically, if the curve is aspiral, that is, a curve having a radial vector R that is a monotonicincreasing function of the radial angle θ, the spiral will be anequiangular spiral if the angle α formed between a radial vector and thetangent for any point P on the spiral is constant.

FIG. 16 illustrates a vaso-occlusive device in accordance with a fourthalternative embodiment, wherein a microcoil 80 has a secondaryconfiguration that resembles a series of interconnected complex curvedsegments 82, each of which is defined by a path around the surface of asphere 84. Each of the segments is thus defined by a unique focus 86located at the approximate center point of the sphere 84 around whichthe path is generated, and by a radius r extending from that locus 86that is equal to the radius of that sphere. Each segment may be definedby radii that are coplanar (in the case of a segment that is defined bya substantially circumferential path around its defining sphere), or byradii that lie in different planes intersecting the sphere (where patharound the defining sphere deviates from a circumferential path). Thesegments thus resemble nearly, but not fully, completed circles(circumferential path) or helical loops (non-circumferential path), andthey may be either of uniform or different diameters.

The present invention thus exhibits several advantages over prior artthree-dimensional microcoils. For example, there is increased coverageof the aneurysm neck, due to the presence of loops across the neck, yetthe probability of any part of the device intruding into the parentartery is reduced. The secondary coil configuration also providessmoother deployment, and, once deployed, the device exhibits greaterresistance to coil compaction, thereby increasing positional stabilityin the face of pulsatile blood flow. This stability is achieved withlower overall friction between the device and the aneurysm wall.Moreover, the random distribution of loops throughout the aneurysmallows the device to maintain a complex shape inside the aneurysm,yielding improved embolization.

While a preferred embodiment and alternative embodiments of theinvention have been described herein, it will be appreciated that anumber of variations and modifications will suggest themselves to thoseskilled in the pertinent arts. For example, other secondaryconfigurations than those described herein may be found that will yieldmost, if not all, of the significant advantages of the invention fortreatment of the typical aneurysm, or that will prove especiallyadvantageous in specific clinical applications. Also, for specificapplications, the dimensions and materials may be varied from thosedisclosed herein if found to be advantageous. These and other variationsand modifications are considered to be within the spirit and scope ofthe invention, as defined in the claims that follow.

1. A vaso-occlusive device comprising a filamentous structure formedinto a minimum energy state secondary configuration comprising aplurality of interconnected, substantially closed loops of progressivelydecreasing diameter from a largest loop to a first smallest loop,wherein the device further comprises a second smallest loop immediatelyadjacent the largest loop, each of the loops defining a discrete axis,whereby the device, in its minimum energy state configuration, definesmultiple axes.
 2. The device of claim 1, wherein each of the loopsdefines a plane and an axis that is substantially perpendicular to theplane.
 3. The device of claim 1, wherein the multiple axes aresubstantially parallel.
 4. The device of claim 1, wherein the closedloops are arranged tangentially to each other.
 5. The device of claim 1,wherein the device is dimensioned for installation in a vascular sitehaving a predetermined maximum dimension, and wherein the device has atleast one dimension, in its secondary configuration, that is at least25% greater than the maximum dimension of the vascular site.
 6. Thedevice of claim 1, wherein the device is dimensioned for installation ina vascular site having a predetermined maximum diameter, and wherein thedevice, in its secondary configuration, has at least one loop having adiameter that is approximately equal to the maximum diameter of thevascular site.
 7. The device of claim 5, wherein the device has alength, in its secondary configuration, that is at least twice themaximum dimension of the vascular site.
 8. The device of claim 1,wherein the filamentous structure is selected from the group consistingof a microcoil, a wire, a slotted wire, a spiral cut wire, a tube, aslotted tube, a spiral cut tube, a polymer filament, a polymer/metalcomposite filament, and a micro-chain.
 9. A vaso-occlusive devicecomprising a filamentous element formed into a minimum energy statesecondary configuration comprising a plurality of interconnected,substantially closed loops of progressively decreasing diameter from alargest loop to a first smallest loop, and wherein the device furthercomprises a second smallest loop immediately adjacent the lamest loop,each of the loops defining a plane and a discrete axis that issubstantially perpendicular to the plane.
 10. The device of claim 9,wherein the axes are substantially parallel.
 11. The device of claim 9,wherein the closed loops are arranged tangentially to each other. 12.The device of claim 9, wherein the device is dimensioned forinstallation in a vascular site having a predetermined maximumdimension, and wherein the device has at least one dimension, in itssecondary configuration, that is at least 25% greater than the maximumdimension of the vascular site.
 13. The device of claim 9, wherein thedevice is dimensioned for installation in a vascular site having apredetermined maximum diameter, and wherein the device, in its secondaryconfiguration, has at least one curved segment having a diameter that isapproximately equal to the maximum diameter of the vascular site. 14.The device of claim 12, wherein the device has a length, in itssecondary configuration, that is at least twice the maximum dimension ofthe vascular site.
 15. The device of claim 9, wherein the filamentouselement is selected from the group consisting of a microcoil, a wire, aslotted wire, a spiral cut wire, a tube, a slotted tube, a spiral cuttube, a polymer filament, a polymer/metal composite filament, and amicro-chain.